1. Field of the Invention:
The present invention relates to a device for starting an occupant crash protector, such as an air bag, a seat belt pretensioner, which detects a vehicle collision and is activated based on the result of detection.
2. Description of the Prior Art:
FIG. 40 is a block diagram showing a conventional device for starting an occupant crash protector, which has been disclosed in JP-A-4/287748, for example. In the drawing, reference numeral 1 indicates an acceleration sensor (hereinafter abbreviated as "G sensor") for outputting a signal about an acceleration developed in the direction of acceleration or deceleration of a vehicle. Reference numeral 1A indicates an integral computing means for obtaining a total acceleration integrated value indicative of a change in vehicle speed, based on the output of the G sensor 1. Reference numeral 2A indicates a first comparing means for comparing the total acceleration integrated value with a threshold level (hereinafter abbreviated as "threshold"). Reference numeral 31 indicates an acceleration direction integrating means for integrating the signal about the acceleration developed in the direction of acceleration of the vehicle, which is outputted from the G sensor 1. Reference numeral 29 indicates a deceleration direction integrating means for integrating the signal about the acceleration developed in the direction of deceleration of the vehicle, which is outputted from the G sensor 1. Reference numeral 3A indicates an integrated-value ratio computing means for computing the ratio of the integrated value in the deceleration direction integrating means 29 to the integrated value in the acceleration direction integrating means 31. Reference numeral 4A indicates a second comparing means for comparing the integrated-value ratio with a threshold. Reference numeral 5A indicates a trigger signal output means for outputting a trigger signal when it is judged in the first comparing means 2A that the total acceleration integrated value increased in the direction of deceleration of the vehicle has exceeded the threshold. Reference numeral 6A indicates a vehicle safety device which is started in response to the trigger signal.
The operation of the device shown in FIG. 40 will now be described.
The G sensor 1 outputs an acceleration developed upon a vehicle collision. The integral computing means 1A integrates the output of the G sensor 1 so as to output a speed signal indicative of a change in vehicle speed. The first comparing means 2A outputs a vehicle-speed change detected signal if the output of the integral computing means 1A is greater than a predetermined threshold.
The acceleration direction integrating means 31 integrates only the signal about the acceleration developed in the direction of acceleration of the vehicle, which is outputted from the G sensor 1. The deceleration direction integrating means 29 integrates only the signal about the acceleration developed in the direction of deceleration of the vehicle, which is outputted from the G sensor 1. The integrated-value ratio computing means 3A produces the ratio of the integrated value in the acceleration direction integrating means 31 to that in the deceleration direction integrating means 29. The second comparing means 4A outputs an acceleration detected signal therefrom if the ratio is greater than a value preset therein. The trigger signal output means 5A outputs a trigger signal when the output of the first comparing means 2A and the output of the second comparing means 4A are both outputted and starts up the vehicle safety device 6A using the trigger signal.
Thus, when this is a shock such that a very large acceleration is alternately developed in the directions of acceleration and deceleration of the vehicle as in the case of an artificial impact or shock (hereinafter called "hammering") which no requires start-up of the vehicle safety device 6A, acts on the vehicle, the integrated-value ratio becomes substantially constant and no outputs is produced from the second comparing means 4A. Therefore, the trigger signal is not outputted from the trigger signal output means 5A.
Since the threshold of the first comparing means 2A is set higher so that the output of the integral computing means 1A does not exceed the threshold of the first comparing means 2A, even if the output of the integrated-value ratio computing means 3A exceeds the threshold upon hammering and the output is produced from the second comparing means 4A, the trigger signal output means 5A does not output a trigger signal.
On the other hand, since the integrated value in the direction of deceleration of the vehicle exceeds the threshold of the first comparing means 2A in a relatively short time when the vehicle actually collides, the trigger signal output means 5A outputs a trigger signal based on the outputs of the first comparing means 2A and the second comparing means 4A so as to promptly activate the vehicle safety device 6A.
Since the conventional starting device is constructed as described above, the shock such as hammering or the like, on which the starting device should not be started, can be detected. The device can distinguish hammering from a shock developed upon the actual collision if the ratio between the integrated values of the signals about the accelerations developed in the directions of acceleration and deceleration of the vehicle is below the predetermined threshold. However, the integrated value in the direction of deceleration of the vehicle becomes greater than the integrated value in the direction of acceleration of the vehicle even if the shock is small, and the ratio between the integrated values often exceeds the predetermined value. In this case, a problem arises such that hammering or the like is misjudged as an actual collision, thus resulting in unnecessary start-up of the starting device. A problem also arises such that if the threshold to be compared with the integrated value is increased to avoid the above problem and make an actual collision decision with satisfactory accuracy, then the actual collision decision is delayed.